Electrochemical-variable speed constant frequency power system

ABSTRACT

A power system which will produce an alternating current output at controlled frequency from a variable frequency power input source. Multiple solid state control devices divide the variable input into incremental voltage controlled pulses which are connected to bipolar electrochemical cells. Then a reference voltage and frequency circuit discharges the electrochemical cells in an order of voltage synchronized with the reference wave form to produce an accurately controlled frequency output.

I United States Patent [1113,568,039

[72] Inventor Milton A. Knight 3,323,076 5/1967 Pelly 321/7X Box113,]!!! l,Centreville, Va. 22020 3,332,002 7/1967 Jollois 321/61 [21]Appl. No. 842,317 3,378,756 4/1968 Potter.... 322/32 [22] Filed July 16,1969 3,419,783 12/1969 Bingley 321/61X [45 1 Patemed 1971 PrimaryExaminer-J. D. Miller Assistant ExaminerGerald Goldberg [541ELECTROCHEMICALNARIABLE SPEED Atjzneys-Edgar J. Brower, Thomas 0.Watson, Jr. and R. R.

CONSTANT FREQUENCY POWER SYSTEM 6 Claims, 5 Drawing Figs.

A power system which produce an alternat. 307/246 ing current output atcontrolled frequency from a variable [5 III. frequency power inputsource Multiple solid state control 0f 60, devi es the variable inputinto incremental voltage con- 61, 68, 69; 320/ 1; 322/ 32; 307/1 10, 2trolled pulses which are connected to bipolar electrochemical cells.Then a reference voltage and frequency circuit [56] References Citeddischarges the electrochemical cells in an order of voltage UNITEDSTATES PATENTS synchronized with the reference wave form to produce anac- 3,152,297 10/1964 Peaslee 321/61 curately controlled frequencyoutput.

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NEG. VOLT. 3RD-4TH D. ELECTRO- EMICAL OUTPUT AA IELECTROCHEMICAL-VARIABLE SPEED CONSTANT FREQUENCY POWER SYSTEM STATEMENTOF GOVERNMENT INTEREST The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for Governmental purposes without the payment of any royaltiesthereon or therefor.

BACKGROUND OF THE INVENTION bustion engines or turbines, usually theprime movers of rotating generators, do not have a constant r.p.m.necessary for an acceptable tolerance limitation in frequency in thegenerator output. One method employed is to introduce a constant speeddrive device between the prime mover and the generator which willmaintain a uniform generator rotation even if the prime mover inputrotational speed varies extensively. This method has not been productiveof the frequency control needed and led to the development of moresophisticated method. One method is the Variable Speed ConstantFrequency (VSCF) system such as developed by General Electric, in whichthe generator produces a very high frequency power output. A controlledfrequency reference is compared against this high frequency output andat every point where the frequency voltage is identical to the generatedvoltage an SCR is switched on to capture a portion of the generatedpower. Since the generator has a frequency many times that of thereference frequency in each reference frequency cycle there will be manysmall portions. These portions have the contour of the frequencyreference and filters shape them into a smooth sine wave. This systemrequires a special high speed oversize generator since only a portion ofthe power generated in each cycle is utilized.

Another VSCF system now in development is one in which the AC power isrectified into DC power and with the use of six inverters, each addingan increment of square wave buildup, a sine wave is formed. However, inthis system the inefficiencies of the rectifier and six inverters areadditive.

The present invention overcomes the disadvantages and shortcomings ofthe prior art systems and offers a power system which, in conjunctionwith the AC output power, contains means for providing power for highsurge or peak loads without strain or overload on the generator, andwhich provides emergency AC and DC power for extended periods of timeafter generator failure.

The electrochemical cells which form an integral part of the conversionare inherently capacitive and will tend to establish a unity powerfactor for any electrical system inductive loading.

This conversion system is slaved to a frequency and voltage signalgenerator and will reproduce the frequency and voltage stipulated by thereference frequency and voltage wave form.

An object of the present invention is a provision of a power systemwhich converts a variable frequency input to a controlled frequencyalternating current output.

Another object is the provision of a power system for providing powerfor high surge or peak loads without strain or overload on the inputgenerator.

Still another object of the present invention is the provision of apower system which will provide emergency AC and DC power for extendedperiods of time after generator failure.

Still another object of the present invention is a provision of a powersystem which exhibits great flexibility with respect to frequency andwave form selection.

Other objects and many of the attendant advantages and novel features ofthe invention will become apparent from the following detaileddescription of the invention when considered in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the manner in which thedrawings may be assembled to provide a complete schematic of theinvention;

FIG. 2(a) shows the circuit components used to sample increments of thegenerator voltage;

FIG. 2b) shows the circuitry for charging the electrochemical cellsduring the first and second quadrants;

FIG. 2(a) shows the circuitry for charging the other cells during thethird and fourth quadrants; and

FIG. 2(d) shows the circuitry for discharging the cells in accordancewith the reference wave form.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingsthere is shown a variable frequency generator 10 which is connectedbetween a generator bus bar 12 and the ground. Generator 10 may be ofany well-known construction and operates at any variable frequency.Connected between the generator bus 12 and ground there are a pluralityof voltage divider circuits consisting of six resistances R1, R2, R3,R4, R5 and R6 these fixed resistances being connected in series withadjustable potentiometers TPl, TF2, TF3, TF4, TF5 and TP6. It may benoted at this point that the number of voltage divider circuitsutilized, as well as the other related stages, will depend upon thenumber of comparisons that are made between the variable frequency inputand a controlled frequency reference voltage, as will be described morefully hereinafter, and for the sake of simplicity only a single channelwill be described fully but it being understood that the remainingchannels operated in a like manner.

Connected between the two resistors R6 and TP6 of the voltage dividercircuit there is a voltage comparator A whose output is connected to ANDgate 14, this element passing the signal on to a series resistor Rl2before applying it to the base of a NPN transistor Q7. NAND gates 24,26, 28, 30 and 32 are connected between the AND gates of each channeland the comparator of the next higher channel. Transistor Q7 has itsemitter element connected to ground and its collector connected to aresistance R19, the other end of this resistance being connected to thebase of a PNP transistor Q1. Resistance R13 connects the base andemitter of transistor Q1 the emitter also being tied to the generatorbus 12. The output of transistor 01, as applied on it's collectorelectrode passes through a diode CR1 before being applied toelectrochemical cell A.

The negative terminal of electrochemical cell A is connected to groundand its second positive terminal is connected to the emitter of a PNPtransistor Q19. The output of transistor Q19 as produced on itscollector electrode passes through a diode CRl3 and is applied to adistribution of utilization bus bar 38.

A controlled frequency reference signal is produced by a signal source34 which may be any wellknown signal generator or other means ofproducing a constant frequency wave form such as 40 and of any desiredfrequency. The output of signal source 34 is applied to a line 36 whichis connected to the base of transistor Q19 to serve as a means forcutting on and off that transistor, and the others as will be definedhereinafter.

The above description has been for the positive voltage for the firstand second quadrants of the sine wave so turn now for a description ofone of the channels for handling the third and fourth quadrants of thenegative portion of the wave. In this situation transistor Q13 has itsbase attached to the generator bus 12 and its collector electrode isconnected to the bus also, but through a rectifier CR7. The emitterelectrode of Ql3'is attached to the negative terminal of electrochemicalcell AA,

and it'should be noted that in this situation the positive electrode isgrounded. The other negative electrode of cell AA is connected to adiode CR19 and this in turn connects to the collector electrode oftransistor Q31 whose emitter electrode is connected todistribution bus38. The base of transistor Q31 is tied to a resistor R41 which in turnis connected to the emitter electrode of transistor Q25 whose base isconnected to a resistance R47 the other terminal of which connects to anAND gate 42. AND gate 42 has input supplied by NAND gate 52 and voltagecomparator circuit AA, the input of voltage comparator AA being tied toone end of potentiometer TP7. Potentiometer TP7 forms, along with fixedresistor R53, a voltage divider circuit which is connected betweenground and the control frequency reference line 36. It should be notedat this point again that the structure just recited in detail above isthat which relates to a single sampling channel, and that the remainingchannels, as for example with electrochemical cells A, B, C... to X, Yand Z, are likewise all connected in the same manner. The number ofchannels chosen depends on the number of samplings it is desired to takeduring one cycle of operation.

Turning now to the operation of the invention it will be observed thatthe invention consists of a conversion system to be used in conjunctionwith a variable speed AC generator and a controlled voltage andfrequency reference device. The system includes multiple solid statecontrol devices which divide the output of the generator intoincremental voltage controlled pulses and feeds these pulses into seriesconnected bipolar electrochemicalcells. The voltage of each pulse willdirect the pulse into a cell which has the same charging voltage as thevoltage of the pulse. The number of pulses per quarter cycle of thegenerator equals the number of electrochemical cells. These pulses setup the double layer capacitance in the electrochemical cells.

The reference voltage and frequency circuit utilizes solid state devicesand circuitry to discharge the double layer capacitance energy of theelectrochemical cells in an order of voltage synchronized with thereference wave form. The third and fourth quadrants of the cycle, beingnegative in direction, requires an identical system as the first andsecond quadrants except that the polarity is reversed. Referring to thedrawings it will be seen that a variable speed generator 10 furnishesvariable frequency power into a generator bus 12. Beginning a cycle at 0voltage, no charging of the electrochemical cells takes place until thebus voltage exceeds A" volts. At this point the lowest AND gate 14produces a 1 output which drives transistors 07 and Q1 into conductionso that current flows from the generator bus 12 through transistor Q1and diode CR1 into electrochemical cell A, thereby allowingelectrochemical cell A to be charged with a double layer capacitance.Charging of A" will continue as long as the voltageon bus 12 is betweenA and B." When the bus voltage exceeds "8 volts transistors Q7 and 01will be turned off because the lower NAND gate 24 will produce a 0"output and thereby disable the Q7 and Q1 transistors. Simultaneouslywith this event Q8 and Q2 will be driven on, and remain on, until thebus voltage exceeds the C voltage. This process will continue through Zvoltage which is the highest voltage of the electrochemical cells. Asthe bus voltage decreases, conduction of the electrochemical cells willpass through each successive voltage stage exactly in the reverse of thevoltage increasing procedure.

On the distribution side of the conversion system the controlledfrequency and voltage reference 34, which produces the output wave form40 onto line 36, controls the action of the cell discharges. Starting atreference voltage 0 no power is discharged into the distribution bus 38from the electrochemical cells. When the reference voltage reaches A"voltage Q19 is turned on and the double layer capacitance of cell A isdischarged into the distribution bus 38 at A voltage through diode CR13.When the reference voltage reaches B volts, 020 is turned on and cell Bdischarges, increasing the voltage of the distribution bus 38 to that ofthe reference voltage at the identical time. Transistor Q19 need not beturned off since the diode rectifier CR13 prevents any power formflowing back into cell A. This process is repeated through cell 2, andas the reference voltage drops the discharges of the cells follows thesame procedures in reverse as when the voltage increased.

During the first and second quadrants of the cycle the voltage ispositive and the negative of the electrochemical cells A through Z isgrounded. On the third and fourth quadrants the voltage is negative andthe positive of electrochemical cells AA through ZZ is grounded. Thismeans that in the third and fourth quadrants of a cycle power flows fromthe generator 10 through ground to the cells and back to the generatorthrough the generator bus 12. On the distribution side during the thirdand fourth quadrants power flows from the cells AA through ZZ throughground to the utilization equipment attached to bus 38 and back to thecells through the distribution bus 12. A separate set of solid statedevices, circuitry and electrochemical cells are used for the third andfourth quadrants. A and D gated 42, 44, 46, 48 and 50 and NAND gates 52,54, 56, 58 and 60 are connected to the frequency and voltage reference34 thereby controlling transistors Q25 through Q36 in the same manner asQ1 through Q12 on the generator bus 12 for the first and secondquadrants. The cells AA through ZZ will be charged from the generator 10by transistor operation controlled by the generator bus 12 negativevoltage during the third and fourth quadrants. The output of thedistribution bus 38 will consist of a series of pulses, equal to twicethe total number of cells per cycle, having the exact wave form andfrequency as the reference 34. These pulses are than fed into a filterfor wave form refinement and other utilization.

The frequency and voltage reference 34 need not be constructed as a partof the conversion system, since the conversion system will duplicate anywave form the frequency reference may have. Thus, very accuratelycontrolled frequency references may be desirable for the system whensupplying power to highly sophisticated equipment, while odd frequenciesand wave forms (sawtooth, square, and so forth) may be desired for otherapplications.

As alternate forms of construction for the invention it is conceivablethat by the development of suitable solid state circuitry, that one setof electrochemical cells and controls would perform all necessaryfunctions. One the cell charging side this is simple, merely by using abridge rectifier giving half wave positive voltage output. Thus, onlyfirst and second quadrant controls are necessary to give the doublelayer capacitance formation in the electrochemical cells. The difficultycomes in the output side however, where the reference cycle would alsobe rectified into half waves and every other half wave discharge of theelectrochemical cells would be inverted to give an AC cycle wave form.

Bipolar electrochemical cells using either rigid or liquid electrodesare preferred since conventional batteries are not practical due totheir high inductance offsetting the double layer capacitance necessaryto make this system work successfully.

From the above description of the structure and operation of theinvention it is obvious that there is presented an entirely new conceptfor combining overload and surge load capability, AC and DC combinationpower, emergency AC and DC power, flexibility of frequency and wave formselection, and usage of available of AC generatorslt has application onany electrical system where frequency control and emergency power isimportant, or where extensive surge or peak loads are experienced.Typical usage would be on mobile power units serving aircraft and radaror missile installations, and the invention can be built as a compactunit with no moving parts and attached to an available AC generator.

Obviously many modifications and variations of the present invention arepossible in light of the above teachings.

lclaim:

1. An electrochemical variable speed constant frequency power systemcomprising:

a source of variable frequency alternating current signals;

means for dividing the signals into incremental pulses;

storage means comprised of electrochemical cells;

means for applying the incremental pulses to the storage means;

a controlled voltage and frequency reference device connected to thestorage means;

an output bus bar; and

means for discharging the storage means into the bus bar in an order ofvoltage synchronized with the reference wave form.

2. The power system of claim 1 wherein the source of variable frequencyalternating current signals is a variable speed alternating currentgenerator.

3. The power system of claim 2 wherein the means for dividing the signalinto incremental pulses comprises a plurality of voltage dividersconnected to the AC generator, the dividers operating in sequence atdifferent potentials, there being a divider for each increment ofvoltage'taken.

4. The power system of claim 3 wherein there is a plurality of solidstate devices connected to the voltage dividers, the solid state devicesbeing forced into conduction by the potential on the voltage dividers.

5. The power system of claim 4 wherein the storage means comprises aplurality of bipolar electrochemical cells capable of exhibiting doublelayer capacitance.

6. The power system of claim 5 wherein the means for discharging thestorage means is a plurality of voltage dividers and solid state deviceswhich are sequentially forced into conduction by the controlled voltageand frequency reference device.

2. The power system of claim 1 wherein the source of variable frequencyalternating current signals is a variable speed alternating currentgenerator.
 3. The power system of claim 2 wherein the means for dividingthe signal into incremental pulses comprises a plurality of voltagedividers connected to the AC generator, the dividers operating insequence at different potentials, there being a divider for eachincrement of voltage taken.
 4. The power system of claim 3 wherein thereis a plurality of solid state devices connected to the voltage dividers,the solid state devices being forced into conduction by the potential onthe voltage dividers.
 5. The power system of claim 4 wherein the storagemeans comprises a plurality of bipolar electrochemical cells capable ofexhibiting double layer capacitance.
 6. The power system of claim 5wherein the means for discharging the storage means is a plurality ofvoltage dividers and solid state devices which are sequentially forcedinto conduction by the controlled voltage and frequency referencedevice.